High-quality-factor Fano resonances in monolayer WS2 coupled with a single dielectric nanosphere at room temperature

Great efforts have been made to explore the Fano resonances in two-dimensional transition metal dichalcogenides (TMDs) coupled with plasmonic nanostructures in the visible region. However, the intrinsic losses of metallic materials and the TMD exciton linewidths of at least tens of meV at room temperature (RT) inevitably limit the achievable Q factor of the Fano resonance. Herein, we integrate a monolayer WS2 with single hydrogenated amorphous silicon nanospheres (SiNSs) in water. Pronounced asymmetric Fano resonances with a Q factor up to 104 at the A exciton frequency (2.0 eV) are observed at RT. Fano fitting and modified coupled-mode theory both suggest a decreased A exciton linewidth of ~10 meV as compared to the reported value (~60 meV). This is attributed to the enhanced decay of trion in WS2. Moreover, directional Fano coupling can be achieved by exciting the hybrid from the SiNS or WS2 side, providing more possibilities in device implementation.